Abstract: Nano-TiO₂/polycarbonate-polypropylene (TiO₂/PC-PP) light diffusion composites were prepared by melt mixing method. The microscopic structure and isothermal crystallization behaviors of nano-TiO₂/PC-PP light diffusion composites were investigated by SEM and DSC, respectively, and the thermal stability and optical property of the composites were investigated. The results show that the average size of the dispersed phase in the optical diffusion system becomes smaller with the addition of nano-TiO₂ and the morphology is more uniform. The half crystallization time of the composites is prolonged, and the overall crystallization rate becomes slower with the increase of mass fraction for nano-TiO₂ in the composites. The addition of nano-TiO₂ makes the initial thermal degradation temperatures and the final residual weights of the composites increase. When the mass fraction of nano-TiO₂ in PP is 5%, the transmittance of the composites is 80% and the haze is 88%, which is the preferably light diffusion performance of the nano-TiO₂/PC-PP light diffusion composites.